1. Field of Invention
The present invention relates to an electroacoustic transducer and a packaging method for the transducer. More particularly, the present invention relates to an underwater wide-band electroacoustic transducer and a packaging method for the transducer.
2. Description of Related Art
Typical active electroacoustic transducer has a tonpilz shape design. FIG. 1 is a schematic diagram showing the side view of a conventional tonpilz-shaped electroacoustic transducer. As shown in FIG. 1, the tonpilz-shaped transducer 100 consists of a plurality of identical dimension piezoelectric ceramic units 102. The piezoelectric ceramic units are chained together using prestress bolt (not shown). FIG. 2 is a graph showing the frequency response of the transducer in FIG. 1. As shown in FIG. 2, a tonpilz-shaped transducer comprising of a series of identical dimension piezoelectric ceramic units can have a single resonance frequency only. Hence, an assembly of identical dimension piezoelectric ceramic units 102 only works in a neighborhood close to the resonance frequency. In other words, the transducer has a narrow frequency bandwidth.
To improve the operating frequency of the tonpilz-shaped transducer 100, a matching layer 104 is often added to the front end of the transmitting surface. FIG. 3 is a schematic diagram showing the side view of a conventional tonpilz-shaped transducer having a matching layer thereon. The matching layer 104 at the front end of the transmitting surface serves to increase operating bandwidth. FIG. 4 is a graph showing the frequency response of the transducer shown in FIG. 3. As shown in FIG. 4, the frequency response has a few peaks. However, material for fabricating the matching layer 104 is difficult to find and the manufacturing process is generally complicated.
In general, a tonpilz-shaped transducer is a package assembled together using compressed rubber pieces. Hence, a relatively large compressive force is often required during the assembling process. However, the ceramic unit is usually formed by powder sintering method and thus has moderate strength only. The exertion of too much pressure may cause unnecessary damages to the piezoelectric ceramic units. Moreover, even an electroacoustic transducer design that incorporates a matching layer still fells short of the target of having an operating frequency bandwidth over several octaves.
Accordingly, one object of the present invention is to provide an underwater wide-band electroacoustic transducer and a packaging method for the transducer. The transducer includes several groups of piezoelectric ceramic units each having a different resonance frequency whose distance of separation is finely adjusted for maximum bandwidth. Moreover, injection-molding method replaces direct compression of rubber during component assembly.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an underwater wide-band electroacoustic transducer. The electroacoustic transducer includes several groups of piezoelectric ceramic units and an acoustic plastic. Each group of piezoelectric ceramic units has a different dimension and separates from a neighboring group by a different distance. Each group of piezoelectric ceramic units contributes a frequency response curve so that together they constitute a frequency response curve with a wide bandwidth. The acoustic plastic is used as an injection-molding compound for joining various piezoelectric ceramic units together into a package.
This invention also provides a method of assembling an underwater wideband electroacoustic transducer. The underwater wide-band electroacoustic transducer comprises of several groups of piezoelectric ceramic units and acoustic window material. To produce the underwater wide-band electroacoustic transducer, groups of piezoelectric ceramic units each having a different dimension are assembled with each ceramic unit separated from each other by different distances. The frequency response of each ceramic unit groups are banded together to produce a package having a wide-band frequency response. The acoustic window material is injected to join the ceramic unit groups together into a package. Thus, groups of ceramic units each having a different dimension and distance of separation from their neighboring groups are assembled into a package having a wide-band frequency response.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.